Nerve graft

ABSTRACT

A nerve graft includes a lyophobic substrate, a carbon nanotube film structure, a protein layer, and a nerve network. The carbon nanotube film structure is located on a surface of the lyophobic substrate. The protein layer is located on a surface of the carbon nanotube film structure away from the lyophobic substrate. The nerve network is positioned on a surface of the protein layer away from the lyophobic substrate.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201010212591.0, filed on Dec. 6, 2010, inthe China Intellectual Property Office, the disclosure of which isincorporated herein by reference. This application is related tocommonly-assigned applications entitled, “NERVE GRAFT,” filed ****(Atty. Docket No. US35622), “METHOD FOR MAKING NERVE GRAFT,” filed ****(Atty. Docket No. US35623), and “METHOD FOR MAKING NERVE GRAFT,” filed**** (Atty. Docket No. US35621).

BACKGROUND

1. Technical Field

The present disclosure relates to a biological graft, especially to anerve graft.

2. Description of Related Art

A nervous system is a complex cellular communication network that ismainly composed of neurons and glial cells (neuroglial cells). Glialcells occupy spaces between neurons and modulate neurons' functions. Theneuron sense features of both external and internal environments andtransmit this information to the brain for processing and storage. Forexample, the neurons receive the diverse types of stimuli from theenvironment (e.g. light, touch, sound) and convert into electricsignals, which are then converted into chemical signals to be passed onto other cells.

Neurons exist in a number of different shapes and sizes, and can beclassified by their morphology and function. The basic morphology of aneuron includes a cell body and neurites projecting/branching from thecell body towards other neurons. The neurites also can be defined intotwo types by their functions. One is a dendrite, which branches aroundthe cell body and receive signals from other neurons to cell body. Theother is an axon, which branches from the cell body and growscontinually without tapering. The axon conducts the signals away fromthe neuron's cell body. The end of the axon has branching terminals thatrelease neurotransmitter substances acting as chemical signals into agap between the branching terminals and the dendrites of other neurons.Thus, the information or signal is propagated.

Once injury to the nervous system occurs, neuron damage will lead toneurite degeneration and retraction. If the damage is severe, breaks inneurites of the neuron are presented. Consequentially, the signaltransmission will be affected and the cellular communication withspecific neurons will cease. Generally, damage on the neurites willreverse by introducing nerve pipes including degradable biologicalmaterial to the nervous system to reconnect with the opposite terminalsin broken neurites. The neurites grow along the nerve pipes until theneurites are combined together. Thus, the neuron damage is reversed.

However, if a distance between the broken neurites is long, a growingtime of the neurites can be long, thus a long recovery time forreversing the neuron damage is required.

What is needed, therefore, is to provide a nerve graft, to overcome theabove-described shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 shows a schematic structural view of a flow chart of oneembodiment of a method for making a nerve graft.

FIG. 2 shows a Scanning Electron Microscope (SEM) image of a flocculatedcarbon nanotube film.

FIG. 3 shows an SEM image of a pressed carbon nanotube film.

FIG. 4 shows an SEM image of a drawn carbon nanotube film.

FIG. 5 shows a side view of the nerve graft.

FIG. 6 shows a top view of the nerve graft.

FIG. 7 shows an SEM image of a carbon nanotube film structure includinga plurality of stacked drawn carbon nanotube films.

FIG. 8 shows a Transmission Electron Microscope (TEM) image of thecarbon nanotube film structure.

FIG. 9 shows a TEM image of a culture layer.

FIG. 10 shows an SEM image of one nerve cell cultured on the culturelayer.

FIG. 11 shows an SEM image of a nerve graft, wherein a nerve network ofthe nerve graft are dyed.

FIG. 12 shows an SEM image of the nerve graft, wherein the nerve networkof the nerve graft are not dyed.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings. It should benoted that references to “an” or “one” embodiment in this disclosure arenot necessarily to the same embodiment, and such references mean atleast one.

A method for making a nerve graft of one embodiment can include thefollowing steps:

S10, providing a culture layer comprising a lyophobic substrate, acarbon nanotube film structure, and a protein layer, the carbon nanotubefilm structure being sandwiched between the lyophobic substrate and theprotein layer;

S20, seeding a plurality of nerve cells on a surface of the proteinlayer away from the lyophobic substrate; and

S30, culturing the plurality of nerve cells until a plurality ofneurites branch from the nerve cells and connect between the pluralityof nerve cells to form a nerve network.

In step S10, the lyophobic substrate is configured to load the carbonnanotube film structure. The lyophobic substrate can improve amechanical strength of the culture layer, and prevent the carbonnanotube film structure from being damaged by an external force. Thelyophobic substrate has a lyophobic property, thus a biological elementsuch as the nerve cell, cannot be cultured in a growth surroundingsupplied by the lyophobic substrate. The lyophobic substrate isinnoxious to a biological element such as the nerve cell, thus thelyophobic substrate can be suitable for loading the nerve network andbeing transplanted into a biological body. In one embodiment, thelyophobic substrate is a silica gel substrate or a substrate coated withsilica gel. The lyophobic substrate can also be a soft substrate, assuch, a shape of the lyophobic substrate can be formed as desired. Theshape of the lyophobic substrate can correspond to a shape of the carbonnanotube film structure.

The carbon nanotube film structure can be capable of forming afree-standing structure. The term “free-standing structure” can bedefined as a structure that does not have to be supported by asubstrate. For example, a free-standing structure can sustain the weightof itself if the free-standing structure is hoisted by a portion thereofwithout any significant damage to its structural integrity. The carbonnanotubes distributed in the carbon nanotube film structure defines aplurality of gaps therebetween. An average gap can be in a range fromabout 0.2 nanometers to about 9 nanometers. The carbon nanotubes canhave a significant van der Waals attractive force therebetween. Thefree-standing structure of the carbon nanotube film structure isrealized by the carbon nanotubes joined by van der Waals attractiveforce. As such, if the carbon nanotube film structure is placed betweentwo separate supporters, a portion of the carbon nanotube film structurenot in contact with the two supporters would be suspended between thetwo supporters and yet maintain film structural integrity.

The carbon nanotubes in the carbon nanotube film structure can beorderly or disorderly arranged. The term ‘disordered carbon nanotubefilm structure’ includes, but is not limited to, a structure where thecarbon nanotubes are arranged along many different directions such thatthe number of carbon nanotubes arranged along each different directioncan be almost the same (e.g. uniformly disordered), and/or entangledwith each other. ‘Ordered carbon nanotube film structure’ includes, butis not limited to, a structure where the carbon nanotubes are arrangedin a consistently systematic manner, e.g., the carbon nanotubes arearranged approximately along a same direction and or have two or moresections within each of which the carbon nanotubes are arrangedapproximately along a same direction (different sections can havedifferent directions). The carbon nanotubes in the carbon nanotube filmstructure can be single-walled, double-walled, and/or multi-walledcarbon nanotubes.

Macroscopically, the carbon nanotube film structure may have asubstantially planar structure. The planar carbon nanotube filmstructure can have a thickness of about 0.5 nanometers to about 100microns. The carbon nanotube film structure includes a plurality ofcarbon nanotubes and defines a plurality of micropores having a size ofabout 1 nanometer to about 500 nanometers. The carbon nanotube filmstructure includes at least one carbon nanotube film, the at least onecarbon nanotube film including a plurality of carbon nanotubessubstantially parallel to a surface of the corresponding carbon nanotubefilm. The carbon nanotube film structure can includes at least onecarbon nanotube film. If the carbon nanotube film structure includes aplurality of carbon nanotube films stacked together. Adjacent carbonnanotube films can only be adhered by van der Waals attractive forcetherebetween.

The carbon nanotube film structure can include a flocculated carbonnanotube film as shown in FIG. 2. The flocculated carbon nanotube filmcan include a plurality of long, curved, disordered carbon nanotubesentangled with each other and can form a free-standing structure.Further, the flocculated carbon nanotube film can be isotropic. Thecarbon nanotubes can be substantially uniformly dispersed in theflocculated carbon nanotube film. The adjacent carbon nanotubes areacted upon by the van der Waals attractive force therebetween, therebyforming an entangled structure with micropores defined therein.Alternatively, the flocculated carbon nanotube film is porous. Sizes ofthe micropores can be about 1 nanometer to about 500 nanometers.Further, due to the carbon nanotubes in the carbon nanotube filmstructure being entangled with each other, the carbon nanotube filmstructure employing the flocculated carbon nanotube film has excellentdurability and can be fashioned into desired shapes with a low risk tothe integrity of the carbon nanotube film structure. The flocculatedcarbon nanotube film, in some embodiments, will not require the use of astructural support due to the carbon nanotubes being entangled andadhered together by van der Waals attractive force therebetween. Theflocculated carbon nanotube film can define a plurality of microporeshaving a diameter of about 1 nanometer to about 500 nanometers.

The carbon nanotube film structure can include a pressed carbon nanotubefilm. The carbon nanotubes in the pressed carbon nanotube film can bearranged along a same direction or arranged along different directions.The carbon nanotubes in the pressed carbon nanotube film can rest uponeach other. The adjacent carbon nanotubes are combined and attracted toeach other by van der Waals attractive force, and can form afree-standing structure. An angle between a primary alignment directionof the carbon nanotubes and a surface of the pressed carbon nanotubefilm can be in a range from approximately 0 degrees to approximately 15degrees. The pressed carbon nanotube film can be formed by pressing acarbon nanotube array. The angle is closely related to pressure appliedto the carbon nanotube array. The greater the pressure, the smaller theangle. The carbon nanotubes in the carbon nanotube film aresubstantially parallel to the surface of the carbon nanotube film if theangle is about 0 degrees. A length and a width of the carbon nanotubefilm can be set as desired. The pressed carbon nanotube film can includea plurality of carbon nanotubes substantially aligned along one or moredirections. The pressed carbon nanotube film can be obtained by pressingthe carbon nanotube array with a pressure head. Alternatively, the shapeof the pressure head and the pressing direction can determine thedirection of the carbon nanotubes arranged therein. Specifically, in oneembodiment, a planar pressure head is used to press the carbon nanotubearray along the direction substantially perpendicular to a substrate. Aplurality of carbon nanotubes pressed by the planar pressure head may besloped in many directions. In another embodiment, as shown in FIG. 3, ifa roller-shaped pressure head is used to press the carbon nanotube arrayalong a certain direction, the pressed carbon nanotube film having aplurality of carbon nanotubes substantially aligned along the certaindirection can be obtained. In another embodiment, if the roller-shapedpressure head is used to press the carbon nanotube array along differentdirections, the pressed carbon nanotube film having a plurality ofcarbon nanotubes substantially aligned along different directions can beobtained. The pressed carbon nanotube film can define a plurality ofmicropores having a diameter of about 1 nanometer to about 500nanometers.

In some embodiments, the carbon nanotube film structure includes atleast one drawn carbon nanotube film as shown in FIG. 4. The drawncarbon nanotube film can have a thickness of about 0.5 nanometers toabout 100 microns. The drawn carbon nanotube film includes a pluralityof carbon nanotubes that can be arranged substantially parallel to asurface of the drawn carbon nanotube film. A plurality of microporeshaving a size of about 1 nanometer to about 500 nanometers can bedefined by the carbon nanotubes. A large number of the carbon nanotubesin the drawn carbon nanotube film can be oriented along a preferredorientation, meaning that a large number of the carbon nanotubes in thedrawn carbon nanotube film are arranged substantially along the samedirection. An end of one carbon nanotube is joined to another end of anadjacent carbon nanotube arranged substantially along the samedirection, by van der Waals attractive force. More specifically, thedrawn carbon nanotube film includes a plurality of successively orientedcarbon nanotube segments joined end-to-end by van der Waals attractiveforce therebetween. Each carbon nanotube segment includes a plurality ofcarbon nanotubes substantially parallel to each other and joined by vander Waals attractive force therebetween. The carbon nanotube segmentscan vary in width, thickness, uniformity, and shape. A small number ofthe carbon nanotubes are randomly arranged in the drawn carbon nanotubefilm and has a small if not negligible effect on the larger number ofthe carbon nanotubes in the drawn carbon nanotube film arrangedsubstantially along the same direction.

Understandably, some variation can occur in the orientation of thecarbon nanotubes in the drawn carbon nanotube film as can be seen inFIG. 3. Microscopically, the carbon nanotubes oriented substantiallyalong the same direction may not be perfectly aligned in a straightline, and some curve portions may exist. Furthermore, it can beunderstood that some carbon nanotubes are located substantially side byside and oriented along the same direction and in contact with eachother.

The carbon nanotube film structure can include a plurality of stackeddrawn carbon nanotube films. Adjacent drawn carbon nanotube films can beadhered by only the van der Waals attractive force therebetween. Anangle can exist between the carbon nanotubes in adjacent drawn carbonnanotube films. The angle between the aligned directions of the adjacentdrawn carbon nanotube films can range from 0 degrees to about 90degrees. In one embodiment, the angle between the aligned directions ofthe adjacent drawn carbon nanotube films is substantially 90 degrees.Simultaneously, aligned directions of adjacent drawn carbon nanotubefilms can be substantially perpendicular to each other, thus a pluralityof micropores and nodes can be defined by the carbon nanotube filmstructure.

The protein layer is positioned on the carbon nanotube film structure toform a hydrophilic and bio-compatible surrounding on the carbon nanotubefilm structure. In one embodiment, the protein layer is located on asurface of the carbon nanotube film structure away from the lyophobicsubstrate. The protein layer can be fibrous protein, enzyme protein, orblood serum. The protein layer can include soluble protein and insolubleprotein. The term “soluble protein” can be defined as a protein capableof interacting with water. In one embodiment, there can be a pluralityof hydrophilic amino acids disposed on the outer surface of the solubleprotein to interact with water. In one embodiment, the protein layerincludes blood serum of a mammal, such as a cow, a pig, or human. Theblood serum cannot only define a hydrophilic and bio-compatiblesurrounding on the carbon nanotube film structure, but can also supply acell growth factor for the nerve cells or the nerve network.

Means for fabricating the culture layer is not limited, provided theprotein layer and the carbon nanotube film structure are mixed together.For example, the culture layer can be fabricated by soaking the carbonnanotube film structure located on the lyophobic substrate with aprotein solution. A volume ratio between the protein and the proteinsolution is from about 50% to about 100%. Thus, the protein solvent canbe a pure protein, or a solution including the protein and a biologicalmedia dissolving the protein.

If the carbon nanotube film structure is soaked by the protein solution,the protein solution can infiltrate into the micropores defined in thecarbon nanotube film structure. Thus, the carbon nanotubes of the carbonnanotube film structure can be soaked by the protein solution.Therefore, the carbon nanotubes can be wrapped by the protein layer.Alternatively, the protein layer can wrap all of the carbon nanotubes orpart of the carbon nanotubes, provided the protein layer can cover atleast part of the surface of the carbon nanotube film structure awayfrom the lyophobic substrate. Thus, the carbon nanotube film structurecan be sandwiched between the protein layer and the lyophobic substrateand need not be in contact with the nerve network directly. The carbonnanotube film structure is a lyophobic article and is not capable ofdefining a hydrophilic and bio-compatible surrounding to form the nervenetwork thereon or acting as a biological substrate. Thus, as long asthe protein layer is located on the carbon nanotube film structure toform the culture layer, the nerve network can be located on the carbonnanotube film structure.

In one embodiment, the culture layer is fabricated by the followingsteps:

S11, providing the lyophobic substrate;

S12, placing the carbon nanotube film structure on a surface of thelyophobic substrate; and

S13, soaking the carbon nanotube film structure located on the lyophobicsubstrate with a protein solution to form the protein layer.

In step S12, the carbon nanotube film structure can cover the surface ofthe lyophobic substrate or be located on part of the surface of thelyophobic substrate. To decrease a specific surface area of the carbonnanotube film structure and increase an adhesive attraction forcebetween the carbon nanotube film structure and the lyophobic substrate,the step S12 can further include the following steps: S121, soaking thecarbon nanotube film structure located on the surface of the lyophobicsubstrate with an organic solvent; and S122, evaporating the organicsolvent out of the carbon nanotube film structure.

In step S13, means for soaking the carbon nanotube film structure withthe protein solution is not limited, provided the protein of the proteinsolution can be adhered to the surface of the carbon nanotube structureto form the protein layer. For example, the protein solution can besprayed on the surface of the carbon nanotube film structure to soak thecarbon nanotube film structure with the protein solution. In oneembodiment, to soak the carbon nanotube film structure with the proteinsolution, the step S13 includes a step of dipping the carbon nanotubefilm structure located on the lyophobic substrate into the proteinsolution. A dipping time is not limited, provided most of the carbonnanotubes of the carbon nanotube film structure are soaked with theprotein solution and the protein does not deteriorate. In oneembodiment, the carbon nanotube film structure is dipped in a cow'sblood serum for about 1.5 hours.

When the carbon nanotube film structure is dipped in the proteinsolution, part of the carbon nanotubes or all of the carbon nanotubescan be soaked by the protein solution. Generally, the greater thedipping time, the more the carbon nanotubes of the carbon nanotube filmstructure can be soaked by the protein solution. The smaller a thicknessof the carbon nanotube film structure, the more the carbon nanotubes ofthe carbon nanotube film structure can be soaked by the proteinsolution.

The step S10 can further include a step of S14, sterilizing the proteinlayer. Means for sterilizing the protein layer is not limited, providednearly all of the bacteria distributed in the protein layer can bekilled. The protein layer can be sterilized by means of an ultravioletsterilization technology or a high temperature sterilization technology.If the protein layer is sterilized by means of high temperaturesterilization technology, a temperature of the protein layer should beless than about 220 degrees, thus the protein layer cannot be damaged.In one embodiment, the temperature of the protein layer is about 120degrees. A rigidity of the protein layer can be increased if the proteinlayer is sterilized because part of the water in the protein layer canbe evaporated.

The step S10 can further include a step of S15: introducing apoly-D-lysine (PDL) layer on a surface of the protein layer away fromthe lyophobic substrate. In the step S15, the poly-D-lysine layer canincrease an adhesive attraction force between the culture layer and thenerve cells by forming a plurality of changes on the surface of theculture layer. The poly-D-lysine layer can be formed by dipping theprotein layer located on the lyophobic substrate into a poly-D-lysinesolution. A concentration of the poly-D-lysine in the poly-D-lysinesolution can be about 20 milligrams per milliliter.

In the step S20, the nerve cells can be from a mammal, such as human, amouse, or a cow. The nerve cells are neurons. In one embodiment, thenerve cells are hippocampal neurons from a mouse. The nerve cells can beseeded on the protein layer by spraying a nerve cells solution to thesurface of the protein layer, or by dipping the culture layer into thenerve cells solution. If the culture layer is dipped into the nervecells solution, the nerve cells solution can be received in a culturedish and the protein layer is not in contact with the culture dish. Inone embodiment, a surface of the lyophobic substrate away from theprotein layer is in contact with the culture dish, to separate theprotein layer and the culture dish. When the protein layer is covered bythe cells solution, the nerve cells in the nerve cells solution can bedeposited or seeded on the surface of the protein layer.

In step S30, surrounding conditions for culturing the nerve cells arenot limited, provided the neurites can branch from the nerve cells andbe connected between the nerve cells. The nerve cells can be culturedunder a room temperature and an ordinary pressure. The nerve cells canalso be cultured under a condition similar to a condition in a mammal.Cell growth factors can be provided by the protein layer to culture thenerve cells. Alternatively, the lyophobic substrate cannot define thegrowth surrounding for the nerve cells, thus, the nerve cells can onlybe cultured on the surface of the carbon nanotube film structure withthe protein layer thereon. The nerve network can only be located on thecarbon nanotube film structure with the protein layer thereon andcombined with the carbon nanotube film structure.

The neurites can include dendrites or axons. Generally, the neurites cangrow in all directions from one nerve cell. But if there are a pluralityof nerve cells located on the surface of the protein layer, the neuritesfrom one nerve cell would preferentially extend to adjacent nerve cells.Thus, growth directions of the neurites can be guided by positions ofthe nerve cells.

In the method for making the nerve graft, the carbon nanotube filmstructure can be sandwiched between the lyophobic substrate and theprotein layer to form the culture layer. The culture layer can define agrow surrounding, thus the nerve network can be formed on the culturelayer. All of the lyophobic substrate, the protein layer and the carbonnanotube film can have a good tactility, nonmetal and biocompatibleproperties, thus the culture layer including the lyophobic substrate,the protein layer and the carbon nanotube film structure can betransplanted into a biological body and form a shape as desired.Therefore, the shape and a thickness of the culture layer can bedesigned as a shape and a thickness of a wound of the biological body,such as a human wound. The nerve cells of the nerve network cancommunicate with each other, thus if the nerve graft is transplantedinto the wound, nerve cells of the biological body close to the woundand the nerve network can be connected together. An area of the woundcan be substantially equal to an area of the nerve graft, and a distancebetween an edge of the nerve graft and an edge of the wound can be lessthan a length of the wound. Therefore, a distance between the nervecells of the biological body close to the wound and the nerve networkcan be less than the length of the wound. The less the distance betweenthe nerve cells of the biological body close to the wound and the nervenetwork, the less the time of connecting the nerve network and the nervecells of the biological body, the less the time recovering the wound.

In addition, generally, the carbon nanotubes are pure carbon nanotubesconsisting primarily of carbon atoms. The carbon nanotubes can alsoinclude carbon nanotubes that are modified, to form a plurality offunctional groups, such as hydrophilic functional groups. But thefunctional groups do not contribute to the method for making the nervegraft, because the functional groups are substantially covered orwrapped by the protein layer.

The nerve graft of one embodiment can be fabricated by the methodmentioned above. Referring to FIG. 5, the nerve graft 100 can include aculture layer 10 and a nerve network 20 located on a surface of theculture layer 10.

The culture layer 10 includes a lyophobic substrate 11, a carbonnanotube film structure 12, and a protein layer 14. The carbon nanotubefilm structure 12 is sandwiched between the lyophobic substrate 11 andthe protein layer 14. The carbon nanotube film structure 12 can bedisposed on one surface of the lyophobic substrate 11, or on twoopposite surfaces of the lyophobic substrate 11. In one embodiment, theculture layer 10 only includes one carbon nanotube film structure 12disposed on one surface of the lyophobic substrate 11.

The lyophobic substrate 11 is configured to load the carbon nanotubefilm structure 12. The lyophobic substrate 11 can improve a mechanicalstrength of the culture layer 10, and prevent the carbon nanotube filmstructure 12 from being damaged by an external force. The lyophobicsubstrate 11 has a lyophobic property, thus a biological element such asthe nerve cell, cannot be cultured in a growth surrounding defined bythe lyophobic substrate 11. The lyophobic substrate 11 is innoxious tothe biological element, such as the nerve cell, thus the lyophobicsubstrate 11 is suitable for being transplanted into a biological body.In one embodiment, the lyophobic substrate 11 is a silica gel substrateor a substrate coated with silica gel. The lyophobic substrate 11 canalso be a soft substrate. As such, a shape or an area of the lyophobicsubstrate 11 can be formed as desired.

Macroscopically, the carbon nanotube film structure 12 is a planarstructure and capable of forming a free-standing structure. The carbonnanotube film structure 12 includes a plurality of carbon nanotubessubstantially parallel to a surface of the corresponding carbon nanotubefilm structure 12. The carbon nanotube film structure 12 can include atleast one carbon nanotube film. If the carbon nanotube film structure 12includes a plurality of carbon nanotube films, the carbon nanotube filmscan be stacked together, and adjacent carbon nanotube films can beadhered by only van der Waals attractive force therebetween. The carbonnanotube film can be a flocculated carbon nanotube film as shown in FIG.2, a pressed carbon nanotube film as shown in FIG. 3, and a drawn carbonnanotube film as shown in FIG. 4. In one embodiment, the carbon nanotubefilm structure 12 includes a plurality of drawn carbon nanotube filmsstacked together. Aligned directions of adjacent drawn carbon nanotubefilms are substantially perpendicular to each other. A thickness of thecarbon nanotube film structure 12 is not limited. Generally, thethickness of the carbon nanotube film structure 12 can be from about 0.3micrometers to about 60 micrometers. In one embodiment, the thickness ofthe carbon nanotube film structure 12 is about 0.6 micrometers.

The protein layer 14 can include fibrous protein, enzyme protein, orblood serum. The protein layer 14 can include soluble protein andinsoluble protein. The term “soluble protein” can be defined as aprotein capable of interacting with water. There can be a plurality ofhydrophilic amino acids disposed on the outer surface of the solubleprotein. In one embodiment, the protein layer 14 includes blood serum ofa mammal, such as a cow, a pig, or human. The blood serum cannot only becapable of defining a hydrophilic and biocompatible surrounding on thecarbon nanotube film structure 12, but also capable of supplying a cellgrowth factor for the nerve cells or the nerve network 20.

A thickness of the protein layer 14 is not limited, provided thehydrophilic and biocompatible surrounding can be defined on the carbonnanotube film structure 12. The thickness of the protein layer 14 can befrom about 0.3 micrometers to about 2 micrometers. In one embodiment,the thickness of the protein layer 14 is about 0.6 micrometers.Macroscopically, the protein layer 14 is located on a surface of thecarbon nanotube film structure 12 away from the lyophobic substrate 11.Microscopically, the protein layer 14 can penetrate into the carbonnanotube film structure 12 and wrap part of or all of the carbonnanotubes of the carbon nanotube film structure 12. Therefore, anobvious interface cannot be defined between the carbon nanotube filmstructure 12 and the protein layer 14. The less the thickness of thecarbon nanotube film structure 12, the more the carbon nanotube filmstructure 12 can be wrapped by the protein layer 14.

The nerve network 20 is disposed on a surface of the protein layer 14away from the lyophobic substrate 11. The neurites 24 can be dendritesor axons. The nerve network 20 includes a plurality of nerve cells 22and a plurality of neurites 24 branching from the nerve cells 22 andconnected among the nerve cells 22. The number of the neurites 24branching from each of the nerve cells 22 is not limited, provided atleast two nerve cells 22 are connected by at least one neurite 24. Eachof the neurites 22 can be connected between two neurites 24, or beconnected to only one neurite 24, provided at least two nerve cells 22are connected by at least one neurite 24.

The culture layer 10 combining with the nerve network 20 can have goodtactility, nonmetal and biocompatible properties, thus the culture layer10 can be transplanted into a biological body, such as human. Thus, ashape and a thickness of the nerve graft 100 can be designed as a shapeand a thickness of a wound of the biological body. The nerve cells 22 ofthe nerve network 20 can communicate with each other by the neurites 24,thus if the nerve graft 100 is transplanted into the wound, nerve cells22 of the biological body close to the wound and the nerve network 20can be connected together. An area of the wound can be substantiallyequal to an area of the nerve graft 100, and a distance between an edgeof the nerve graft 100 and an edge of the wound can be less than thelength of the wound. Therefore, a distance between the nerve cells 22 ofthe biological body close to the wound and the nerve network 20 can beless than the length of the wound. The less the distance between thenerve cells 22 of the biological body close to the wound and the nervenetwork 20, the less time it takes to connect the nerve network 20 andthe nerve cells 22 of the biological body with the neurites 24, and theless the time it takes for the wound to heal.

A method for making a nerve graft of one detailed embodiment can includethe following steps:

S210, providing a silica gel substrate;

S220, placing a carbon nanotube film structure on a surface of thesilica gel substrate;

S230, dipping the silica gel substrate with the carbon nanotube filmstructure placed thereon into a cow's blood serum to soak the carbonnanotube film structure with the cow's blood serum, thus allowing acow's blood serum layer to form the carbon nanotube film structure;

S240, taking the silica gel substrate with the carbon nanotube filmstructure and the cow's blood serum layer placed thereon out of thecow's blood serum solution, and sterilizing the cow's blood serum layerunder a temperature of about 120 degrees;

S250, dipping the sterilized cow's blood serum layer into apoly-D-lysine solution to form a poly-D-lysine layer on the cow's bloodserum layer, and thus a culture layer including the silica gelsubstrate, the carbon nanotube film structure, the protein layer, andthe poly-D-lysine layer is formed;

S260, covering the culture layer with a nerve cell solution until aplurality of nerve cells 22 dissolved in the nerve cell solution aredeposited on a surface of the poly-D-lysine layer away from thelyophobic substrate; and

S270, culturing the plurality of nerve cells 22 until a plurality ofneurites 24 branch from the nerve cells 22 and are connected among theplurality of nerve cells 22.

In step S210, the silica gel substrate includes silica gel. The silicagel is innoxious to the biological element, such as the nerve cell.Thus, the silica gel substrate can be suitable for loading the nervenetwork and transplanted into a biological body to recover a nervoussystem. The silica gel substrate is also a soft substrate. A shape or anarea of the silica gel substrate can be formed as desired. The shape ofthe silica gel substrate can correspond to a shape of a wound of thenervous system, and the area of the silica gel substrate can correspondto an area of the wound of the nervous system.

In step S220, to decrease a specific surface area of the carbon nanotubefilm structure and increase an adhesive attraction force between thecarbon nanotube film structure and the silica gel substrate, the stepS220 can further include the following steps: S221, soaking the carbonnanotube film structure located on the surface of the lyophobicsubstrate with an organic solvent; and S222, evaporating the organicsolvent out of the carbon nanotube film structure. Referring to FIG. 7and FIG. 8, the carbon nanotube film structure includes a plurality ofdrawn carbon nanotube films stacked together; aligned directions ofadjacent drawn carbon nanotube films are substantially perpendicular toeach other.

In step S230, the cow's blood serum is pure liquid cow's blood serum.When the carbon nanotube film structure is dipped into the cow's bloodserum, the carbon nanotube film structure is difficult to be damaged bya surface tension of the cow's blood serum because of the support of thesilica gel substrate. A dipping time for dipping the carbon nanotubefilm structure can be determined by a thickness of the carbon nanotubefilm structure. The less the thickness of the carbon nanotube filmstructure, the shorter the dipping time. In one embodiment, thethickness of the carbon nanotube film structure is about 0.6micrometers, and the dipping time is about 1.5 hours. If the carbonnanotube film structure has a thickness of about 0.6 micrometers dippedin the cow's blood serum for about 1.5 hours, the cow's blood serumlayer can be formed on the carbon nanotube film structure as shown inFIG. 9.

A rigidity of the protein layer can be increased if the protein layer issterilized under the temperature, because part of the water in theprotein layer can be evaporated.

In the step S250, the poly-D-lysine layer is disposed on a surface ofthe cow's blood serum layer away from the lyophobic substrate. Thepoly-D-lysine layer can increase an adhesive attraction force betweenthe culture layer and the nerve cells by forming a plurality of changeson the surface of the culture layer. A concentration of thepoly-D-lysine in the poly-D-lysine solution can be about 20 milligramsper milliliter.

In the step S260, the nerve cells 22 can be from a mammal, such as ahuman, a mouse, or a cow. The nerve cells 22 are neurons. In oneembodiment, the nerve cells22 are hippocampal neurons from a mouse. Ifthe culture layer is dipped into the nerve cells solution, the nervecells solution can be received in a culture dish and the cow's bloodserum layer is not in contact with the culture dish. In one embodiment,a surface of the lyophobic substrate away from the cow's blood serumlayer is in contact with the culture dish to separate the cow's bloodserum layer and the culture dish. When the cow's blood serum layer iscovered by the cells solution, the nerve cells in the nerve cellssolution can be deposited or seeded on the surface of the cow's bloodserum layer.

In step S270, surrounding conditions for culturing the nerve cells 22are not limited, provided the neurites 24 can branch from the nervecells 22 and be connected between the nerve cells. The nerve cells 22can also be cultured under room temperature and an atmospheric pressure.The nerve cells can be cultured under a condition similar to a conditionin a mammal Referring to FIG. 10, when one of the nerve cells 22 seededon the culture layer are cultured in a typical room condition for about15 days, a plurality of neurites 24 branch from one of the nerve cells.

The neurites 24 can be dendrites or axons. Generally, the neurites 24can grow in all directions from one nerve cell. Referring to FIG. 11 andFIG. 12, if there are a plurality of nerve cells located one the surfaceof the cow's blood serum layer, the neurites from one nerve cell wouldpreferentially extend to adjacent nerve cells. Thus, growth directionsof the neurites can be guided by positions of the nerve cells. The nervecells can also be connected by the neurtites to form the nerve network.Cell growth factors can be provided by the cow's blood serum layer forculturing the nerve cells. Alternatively, the lyophobic substrate cannotdefine the growth surrounding for the nerve cells, the nerve cells canonly be cultured on the surface of the carbon nanotube layer with cow'sblood serum layer thereon. The nerve network can only be located on thecarbon nanotube layer with cow's blood serum layer thereon and combinedwith the carbon nanotube layer.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

It is to be understood that the above-described embodiments are intendedto illustrate rather than limit the disclosure. Any elements describedin accordance with any embodiments is understood that they can be usedin addition or substituted in other embodiments. Embodiments can also beused together. Variations may be made to the embodiments withoutdeparting from the spirit of the disclosure. The above-describedembodiments illustrate the scope of the disclosure but do not restrictthe scope of the disclosure.

1. A nerve graft, comprising: a lyophobic substrate, a carbon nanotubefilm structure located on a surface of the lyophobic substrate; aprotein layer located on a surface of the carbon nanotube film structureaway from the lyophobic substrate; and a nerve network positioned on asurface of the protein layer away from the lyophobic substrate; whereinthe nerve network comprises a plurality of nerve cells and a pluralityof neurites branching from the nerve cells and connected between theplurality of nerve cells to form the nerve network.
 2. The nerve graftof claim 1, wherein the lyophobic substrate is a silica gel substrate ora substrate coated with silica gel.
 3. The nerve graft of claim 1,wherein the carbon nanotube film structure comprises a carbon nanotubefilm comprising a plurality of carbon nanotubes substantially parallelto a surface of the carbon nanotube film.
 4. The nerve graft of claim 3,wherein the carbon nanotube film is a flocculated carbon nanotube film,a pressed carbon nanotube film, or a drawn carbon nanotube film.
 5. Thenerve graft of claim 3, wherein the carbon nanotube film structurecomprises a plurality of carbon nanotube films, adjacent carbon nanotubefilms being combined and attracted to each other only by van der Waalsattractive force therebetween.
 6. The nerve graft of claim 1, whereinthe carbon nanotube film structure includes a plurality of carbonnanotubes, a majority of the plurality of carbon nanotubes are orientedalong a preferred orientation.
 7. The nerve graft of claim 6, wherein amajority of the plurality of neurites are oriented along the preferredorientation.
 8. The nerve graft of claim 1, wherein the protein layercomprises soluble protein.
 9. The nerve graft of claim 1, wherein theprotein layer comprises fibrous protein, enzyme protein, blood serum, orcombinations thereof.
 10. The nerve graft of claim 9, wherein theprotein layer comprises blood serum of a cow.
 11. The nerve graft ofclaim 1, wherein the protein layer penetrates into the carbon nanotubefilm structure.
 12. The nerve graft of claim 1, wherein the carbonnanotube film structure comprises a plurality of carbon nanotubes, andthe protein layer wraps part of or all of the carbon nanotubes of thecarbon nanotube film structure.
 13. The nerve graft of claim 1, whereina thickness of the protein layer is from about 0.3 micrometers to about2 micrometers.
 14. The nerve graft of claim 1, wherein each of theplurality of nerve cells is connected to an adjacent nerve cell of theplurality of nerve cells by at least one of the plurality of neurites.15. The nerve graft of claim 1, wherein the plurality of neuritescomprise dendrites and axons.
 16. The nerve graft of claim 1, wherein anarea of a cross-section of the nerve graft substantially parallel to thesurface of lyophobic substrate is greater than 15×15 square millimeters.17. The nerve graft of claim 1, further comprising a poly-D-lysine layerdisposed between the protein layer and the nerve network.
 18. A nervegraft, comprising: a culture layer comprising a lyophobic substrate anda composite carbon nanotube film structure located on a surface of thelyophobic substrate, the composite carbon nanotube film comprising aplurality of carbon nanotubes and a protein layer; and a nerve networkpositioned on a surface of the composite carbon nanotube film structureaway from the lyophobic substrate, the nerve network comprising aplurality of nerve cells and a plurality of neurites connected among theplurality of nerve cells; wherein at least part of the plurality ofcarbon nanotubes are wrapped by the protein layer.
 19. The nerve graftof claim 18, wherein the plurality of nerve cells and the plurality ofneurites are located on the protein layer other than directly located onouter surfaces of the carbon nanotubes.
 20. A nerve graft, comprising: aculture layer comprising a lyophobic substrate and a composite carbonnanotube film structure located on a surface of the lyophobic substrate,the composite carbon nanotube film being composited by a carbon nanotubefilm structure and a protein layer; and a nerve network positioned on asurface of the composite carbon nanotube film structure away from thelyophobic substrate, the nerve network comprising a plurality of nervecells and a plurality of neurites connected among the plurality of nervecells.